Overleaf can work with graphics, you just have to upload them via Project -> Files -> Upload from computer. You have to be logged in, though.

MikTeX currently has some problems with the repositories, there have been some changes. Doing a basic install isn't recommended these days, as disk space is fairly cheap. Better use the complete installation. An alternative to MikTeX, which also works with Linux and MaC is TeX Live. The full installation is default and the software is maintained by the worldwide user group called TUG.

If you decide for an offline installation, it will in general need 2 to four hours for a complete isntall, depending on the internet connection.

The smart way: Calm down and take a deep breath, read posts and provided links attentively, try to understand and ask if necessary.